1. muriatic acid ,zonrox and chlorine are substances used as stain remover. when are these substances harmful?

If used on sensitive parts in large amount.

Explanation:

If these substances are taken in by an individual, it become harmful because these substances are not eating purpose, they are used for cleaning purpose. these substances are harmful when used in large amount on the sensitive parts of the body such as eyes and skin etc. So we can say that these substances are harmful when taken as food and contact with sensitive parts of the body.

i am going to guess that it is co2.

every el niño cycle is different. every year.